Method for performing in vivo dosimetry

• US 20050151071A1
• Filed: 05/06/2003
• Published: 07/14/2005
• Est. Priority Date: 05/06/2002
• Status: Active Grant

• Current Assignee: Gorgen Nilsson
• Original Assignee: Gorgen Nilsson
• Inventors: Nilsson, Gorgen
• Granted Patent: US 7,345,274 B2
• Time in Patent Office: Days
• US Class Current: 250/252.100
• CPC Class Codes: A61N 2005/1076 using a dummy object placed in the radiation field, e.g. phantom
• CPC Class Codes: A61N 5/1042 with spatial modulation of the radiation beam within the treatment head
• CPC Class Codes: A61N 5/1048 Monitoring, verifying, controlling systems and methods
• CPC Class Codes: A61N 5/1071 for verifying the dose delivered by the treatment plan

Abstract

The present invention relates to a method enabling quantification of dose delivery in radiotherapy treatment during patient-specific treatment of the patient utilising measurements in predefined time-intervals with information means positioned in the radiation beam, between the patient and the source and converting the readings to corresponding measures in a phantom. The invention additionally covers the method to obtain the said calibration factors for the detectors. The said calibration factors are obtained for each information means, field and said definable time-interval simultaneously irradiating the information means and said phantom including detectors to measure the absorbed dose using the said patient-specific treatment without patient.

Claims

1. Method for enabling quantification of dose delivery in radiotherapy treatment, characterised in that it comprises the steps of

irradiation of a phantom,

measurement in said phantom,

collecting information regarding the irradiation by information means arranged between the phantom and the radiation source, wherein said measurements are divided in time-intervals, and

analysing the measurements for obtaining information regarding the relationship between the measurements in the phantom and the information between the phantom and the treatment source at each time-interval, which relationship information is to be used as verification of, the treatment of the patient.

2. Method according to claim 1, characterised in that the information means comprises the position of Multi Leaf Collimator leafs (MLC) arranged for shaping the irradiating beam of the radiation source.

3. Method according to claim 2, characterised in that the measurements in the phantom and the determination of the positions of Multi Leaf Collimator leafs are performed simultaneously.

4. Method according to claim 1, characterised in that the information means comprises detectors (ExtDet).

5. Method according to claim 4, characterised in that the measurements in the phantom and with detectors (ExtDet) are performed simultaneously.

6. Method according to claim 2 to 5, characterised in calculating calibration factors from the obtained relationship information as the ratio of the reading from information from the information means and the measurements along the radiation ray in the phantom.

7. Method according to any of the preceding claims, characterised in the further step of storing the data for each specific time-interval both for measurements in the phantom and information between the patient and the treatment source.

8. Method according to claim 6 when dependent on claim 4 or 5, characterised in that the calibration factor are calculated according to

Cal_n,f,seg−

n,f,p,t(i),t(i+1)=S_{n,f,t(i),t(i+1)}/(D<sub>seg−

n,f,p,t(i),t(i+1)</sub>)

where

D<sub>seg−

n,f,p,t(i),t(i+1)</sub> The dose in point p in the phantom-segment defined by the DetExt detector-element, n and the field (projection), f integrated from time t(i) until t(i+1)

S_{n,f,t(i),t(i+1)} The signal from the ExtDet detector-element, n, in the field, f, integrated from time t(i) until t(i+1)

Cal<sub>n,f,seg−

n,f,p,t(i),t(i+1)</sub> The calibration factor to be used with ExtDet detector-element n, in the field, f. To convert the signal integrated from time t(i) until t(i+1) to achieve the dose in the point p in the phantom-segment defined by the DetExt detector-element, n and the field (projection), f integrated from time t(i) until t(i+1)

9. Method according to any of the claims 4 to 8, characterised in that the detectors (ExtDet) are positioned on the surface of the phantom.

10. Method according to any of the claims 4 to 8, characterised in that the detectors (ExtDet) are positioned between the radiation source and the surface of the phantom.

11. Method according to any of the claims 5 to 7, wherein the detectors (ExtDet) are placed inside the phantom.

12. Method according to claim 6 when dependent on claim 2 or 3, characterised in that the calibration factors are calculated according to

Cal_{n,f,p,t(i),t(i+1)}=F_{n,f,t(i),t(i+1)}/(D_{f,p,t(i), t(i+1)})

where

D_{f,p,t(i),t(i+1)} The dose in point p in the phantom at the field (projection), f integrated from time t(i) until t(i+1)

F_{n,f,t(i),t(i+1)} The radiation fluency in the field, f, between the patient and the source along the ray that intersects point p in the phantom integrated from time t(i) until t(i+1)

Cal_{n,f,p,t(i),t(i+1)} The calibration factor describing the relation between the fluency between the patient and the source and the dose in the phantom.

13. Method according to any of the preceding claims, characterised in using a patient specific treatment plan during irradiation of the phantom, and verification of the accuracy of the irradiation of the phantom comparing the measured dose in the phantom with the treatment plan.

14. Method according to claim 2 or 3, characterised in, during treatment of the patient, utilising the same positions of the MLC'"'"'s as during the irradiation of the phantom.

15. Method according to any of the preceding claims 1, 4-11, characterised in, during treatment of the patient, utilising ExtDet in the same lateral positions between the patient and the treatment source as during the irradiation of the phantom.

16. Method according claim 15, characterised in, during treatment of patient, converting the readings from ExtDet to dose using said calibration factors for each time-interval.

17. Method according to claim 16, characterised in that the readings are converted according to:

D <sub>seg−

n,f,p,t(i),t(i+1)</sub> =S _{n,f,t(i),t(i+1)} /Cal <sub>n,f,seg−

n,f,p,t(i),t(i+l)</sub>

18. Method according to claim 12, characterised in, during treatment of the patient, converting the information from the positions of the MLC'"'"'s to dose using said calibration factors for each time-interval.

19. Method according to claim 18, characterised in that the readings are converted according to:

D _{f,p,t(i),t(i+1)} =F _{n,f,t(i),t(i+1)} /Cal _{n,f,p,t(i), t(i+1)}

20. Method according to any of the claims 16 to 19, characterised in totalising the readings from all time-intervals for each specific dose point in order to obtain the total dose.

21. Method according to claim 20 when dependent on claims 16-17, characterised in that the totalisation is obtained according to:

$\begin{array}{c}{D}_{\mathrm{seg}-n,f,p}=<br><br>\underset{i=0<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{to}<br><br>\text{\hspace{1em}<br><br>}<br><br>T}{\sum <br><br>}<br><br>D_{\mathrm{seg}-n,f,p,t<br><br>\left(i\right),t<br><br>\left(i+1\right)}<br><br>\text{)}\\ =<br><br>\underset{i=0<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{to}<br><br>\text{\hspace{1em}<br><br>}<br><br>T}{\sum <br><br>}<br><br>\left(S_{n,f,t<br><br>\left(i\right),t<br><br>\left(i+1\right)}/{\mathrm{Cal}}_{n,f,\mathrm{seg}-n,f,p,t<br><br>\left(i\right),t<br><br>\left(i+1\right)}\right)\end{array}$

22. Method according to claim 20 when dependent on claims 18-19, characterised in that the totalisation is obtained according to:

$\begin{array}{c}{D}_{f,p}=<br><br>\underset{i=0<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{to}<br><br>\text{\hspace{1em}<br><br>}<br><br>T}{\sum <br><br>}<br><br>D_{f,p,t<br><br>\left(i\right),t<br><br>\left(i+1\right)}\\ =\underset{i=0<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{to}<br><br>\text{\hspace{1em}<br><br>}<br><br>T}{\sum <br><br>}<br><br>F_{n,f,t<br><br>\left(i\right),t<br><br>\left(i+1\right)}/{\mathrm{Cal}}_{n,f,p,t<br><br>\left(i\right),t<br><br>\left(i+1\right)}\end{array}$

23. Method according to claim 4, comprising the further step of determining the position of the ExtDet in the transversal plane using the projection of the detectors or markers well defined to the ExtDet utilising an image from an image device down streams the phantom e.g. EPID or radiographic film.

25. Computer program product capable of enabling a computer perform the method according to any of the claims 1 to 24.

26. Computer program product according to claim 25, stored on a computer readable media.

24. Method according to any proceeding claims, characterised in using the dose distribution in a patient at one treatment fraction or accumulated for several treatment fractions, where the dose distribution is obtained by calculations using measurement of the patient anatomy and delivered dose, to modify the subsequent treatments due to previous treatments in order to adapt the intended dose distribution.